Identification and Control Methods of Diseases in the Seedling Stage of Panax notoginseng

Because Panax notoginseng grows year-round in a shaded and humid environment, diseases such as black spot, round spot, phytophthora blight, rust rot and powdery mildew occur and cause serious damage, with annual losses from various diseases reaching 30%-40%, and in severe cases over 80%. The stage of emergence and leaf growth, when the plant is tender, the root system is underdeveloped and stress resistance is poor, is an important period for initial infection by many pathogens. If spring rain comes early and frequently, the disease spreads rapidly and the damage and losses are severe. Panax notoginseng generally takes 60-75 days from sowing to emergence, and strengthening field management during this period to promote vigorous growth of Panax notoginseng is closely related to controlling the occurrence and development of diseases. Therefore, seizing the opportunity and carrying out integrated control to curb the occurrence and harm of diseases in the seedling stage of Panax notoginseng is the key to integrated disease control of Panax notoginseng. The main measures are:

1. Drought-resistant watering, waterlogging prevention and moisture drainage. As the saying goes, "water is the life of notoginseng, and also its disease," meaning that both too much and too little water are harmful to the growth of Panax notoginseng. If soil moisture is insufficient or there is drought, the sown Panax notoginseng seeds will dry out and become "hollow seeds," and the seed strips will also soften, then shrink and become moldy, all of which prevent normal emergence. Therefore, for dry land, watering timely and in appropriate amounts according to soil moisture, preventing overwatering and avoiding alternating drought and wetness; and for low-lying land, dredging ditches and draining promptly, are the keys to ensuring normal emergence of Panax notoginseng, improving plant disease resistance and reducing disease occurrence.

2. Adjusting the shade shed. According to the light requirements of Panax notoginseng of different ages and the characteristics of seasonal changes, repairing and adjusting the shade shed to meet the light requirements of Panax notoginseng is also an important measure to promote vigorous growth and control the occurrence and development of diseases.

3. Removing weeds. Weeds compete with Panax notoginseng for nutrients, water and space, greatly affecting its growth. At the same time, weeds are also hosts of many pathogens. Therefore, timely removal of weeds can promote vigorous growth of Panax notoginseng and reduce the development and spread of diseases.

4. Reasonable topdressing. After the emergence of Panax notoginseng, reasonable topdressing should be carried out according to soil fertility, base fertilizer conditions and seedling condition, with a ratio of nitrogen 2, phosphorus 1 and potassium 3. It is advocated to apply small amounts multiple times, apply nitrogen, phosphorus and potassium together, and appropriately increase potassium fertilizer to improve plant disease resistance.

5. Chemical control. Before the emergence of Panax notoginseng, use 1 part carbendazim plus 1 part thiophanate, diluted 500-600 times with water, or use 5 degrees Baume lime-sulfur mixture to disinfect the bed surface once, with each application 10-15 days apart, which can prevent powdery mildew and many other diseases. After emergence, inspect frequently. Once central infected plants are found, mark them, remove the diseased and residual plants, and then carry out targeted control. The following agents and formulas may be selected as appropriate and sprayed evenly, once every 7-10 days, for 2-3 consecutive applications.

To control damping-off of seedlings, use 30% hymexazol 1000-fold solution, or 50% carbendazim 200-400-fold solution, or 1:1:150 Bordeaux mixture for spraying or drenching, which can block the center of infection and control the spread of the disease.

To control diseases of two- and three-year-old Panax notoginseng seedlings, the main diseases include phytophthora blight, black spot, round spot, anthracnose, rust rot, powdery mildew and stem rot. Before emergence, spray 20% thiophanate plus 70% thiophanate-methyl 800-1000-fold solution, or 50% carbendazim plus 70% mancozeb 600-fold solution, or carbendazim plus thiram 800-fold solution, which can prevent diseases or reduce damage. After the emergence of Panax notoginseng, inspect frequently. Once the center of infection is found, clean it up and block it promptly, and select the following agents for timely control.

① To control black spot of Panax notoginseng, spray 1.5% polyoxin 150-200-fold solution, or 75% chlorothalonil 500-600-fold solution, or 40% dimethachlon 400-fold solution.

② To control round spot of Panax notoginseng, spray 30% difenoconazole 2500-fold solution, or 10% polyoxin plus 50% procymidone 1500-fold solution, or 60% Shida 800-fold solution.

③ To control phytophthora blight of Panax notoginseng, spray 80% fosetyl-aluminium 500-fold solution, or 72% cymoxanil 550-fold solution, or 58% metalaxyl-mancozeb 500-fold solution, or 64% oxadixyl-mancozeb 500-fold solution.

④ To control anthracnose of Panax notoginseng, spray 70% mancozeb 500-fold solution, or 70% thiophanate-methyl 1000-fold solution, or 30% pyrimethanil 1000-fold solution.

At the seedling stage of Panax notoginseng, two or more diseases often occur at the same time. Therefore, according to the condition of the disease, it is advocated to mix fungicides with different characteristics in order to reduce the number of sprayings, expand the target of control, lower control costs and improve control efficiency.